共查询到20条相似文献,搜索用时 18 毫秒
1.
T. M. Roshchina N. K. Shonia M. S. Lagutova V. Yu. Borovkov L. M. Kustov A. Yu. Fadeev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(7):1128-1135
Diffuse reflection IR spectroscopy, static adsorption, and gas chromatography were used to study the chemistry and adsorption properties of the surface of silicas modified by chemically grafted bi-(C6F13(II)) and trifunctional (C6F13(III)) perfluorohexylsilanes. It was established that the modification of silica (SiO2) results in a nearly complete screening of free silanols. At the same time, IR spectra featured absorption bands belonging to weakly perturbed OH groups capable of interacting with benzene molecules. The IR spectroscopy data on benzene adsorption were found to be in close agreement with the results of static adsorption and chromatographic measurements, according to which the specific amount of benzene adsorbed decreases in the series SiO2 > C6F13(III) > C6F13(II). It was demonstrated that the heat of adsorption of benzene on the C6F13(III) sample is higher than that on the initial carrier. Grafted layers prepared from the trifunctional modifier exhibited higher efficiency in preventing benzene molecules from reaching the carrier surface. 相似文献
2.
Kunimitsu Morishige 《Adsorption》2008,14(2-3):157-163
We review some recent progress in experimental studies of the adsorption hysteresis of simple molecules in ordered mesoporous
silicas. We show that the nature of the adsorption hysteresis due to capillary condensation can be examined with less ambiguity
by measuring the hysteresis loop for the ordered mesoporous silicas with three types of pore geometries (cylindrical, interconnected
cylindrical, and interconnected spherical) over a wide temperature range. The adsorption hysteresis arises from the metastability
of a confined phase and the temperature at which the hysteresis disappears is lower than the critical temperature of vapor-liquid
equilibrium in pores. The hysteresis occurs mainly on the desorption rather than adsorption branch, irrespective of the pore
geometries. 相似文献
3.
T. M. Roshchina T. A. Kuznetsova M. S. Lagutova A. M. Tolmachev 《Moscow University Chemistry Bulletin》2007,62(4):187-190
Adsorption of various classes of organic compounds has been studied on silicas chemically modified by silanes that contain a trimethylsilyl group: (CH3)3Sil(TMS) and (CH3)3Si(CH2)3(CH3)2SiCl (C3TMS). The effect caused by the nature of the adsorbate and grafted groups on the thermodynamic parameters of adsorption has been studied. Surface modifying is shown to dramatically decrease the Henry constants of n-alkane adsorption equilibrium relative to the unmodified matrix. The contribution of specific interactions to adsorption, estimated by different methods, in the TMS-silica sample is higher than in the C3TMS-silica sample. 相似文献
4.
T. D. Khokhlova E. V. Vlasenko D. N. Khryashchikova S. N. Lanin V. V. Smirnov 《Moscow University Chemistry Bulletin》2011,66(2):83-87
Ag0 and Ag(I) nanoparticles are immobilized on the surface of a macroporous silica and amino silica. The adsorption kinetics
of a basic dye, methylene blue (MB), from aqueous solutions and the adsorption isotherms of alkyne phenylacetylene from an
octane solution are measured. The dependence of the rate constants of MB adsorption on the conditions of immobilization and
silver reduction is considered. Silica containing immobilized Ag(I) is shown to have a high adsorption activity with respect
to phenyl acetylene. By gas chromatography, it is shown that silver-modified silica has a higher selectivity with respect
to alkenes. The reduction of silver on the silica surface and the complexation of silver ions with aminopropyl groups of amino
silica lead to a significant decrease in the selectivity of composites. 相似文献
5.
M Borówko S Sokołowski T Staszewski Z Sokołowska JM Ilnytskyi 《The Journal of chemical physics》2012,137(7):074707
We apply density functional theory to study adsorption of ions, treated in the framework of the restricted primitive model (RPM), on surfaces modified by tethered polyampholytes. The residual electrostatic contribution to the free energy functional is approximated by using the approach proposed by Wang et al. [J. Phys.: Condens. Matter 23, 175002 (2011)] for simple nonuniform RPMs systems. Our research concentrates on the problems how the distribution of the charges within chains of polyampholytes changes the selectivity of adsorption of ions species, the structure of the surface layer, and its electric properties. 相似文献
6.
Adsorption of 1-butanol from water on modified silicate surfaces 总被引:1,自引:0,他引:1
The structure and the sorption properties of partially hydrophobized silicates (dodecylammonium and dodecyldiammonium vermiculites) have been investigated in aqueous solutions of 1-butanol. The alcohol is preferentially adsorbed on the surface. The interlayer composition is calculated from adsorption and x-ray diffraction data. In air-dried state the organic cations lie flat on the interlamellar surface. In aqueous butanol solutions, the basal spacing of dodecylammonium vermiculite gradually increases with the extent of butanol adsorption because the chains increasingly point away from the surface. The basal spacing of dodecyldiammonium vermiculite is virtually independent on the interlayer composition because the expansion of the interlayer space is sterically restricted and a relatively rigid structure is formed. The enthalpy of the displacement of water by 1-butanol has been determined by flow sorption microcalorimetry. The displacement process is endothermic. 相似文献
7.
Atsuko Yoshida Norishige Kakegawa Makoto Ogawa 《Research on Chemical Intermediates》2003,29(7-9):721-731
The adsorption of a cationic porphyrin, tetrakis-(N-methyl-4-pyridiniumyl)porphine, into mesoporous silicas from solution of tetrakis-(N-methyl-4-pyridiniumyl)porphine p-toluene sulfonate was investigated. Irrespective of the pore size (2.4, 3.5 and 4.2 nm), the cationic porphyrin was adsorbed effectively onto mesoporous silicas to give brown-colored powders. Depending on the amounts adsorbed, which correlate with the average intermolecular distance, the porphines tend to aggregate (dimer). 相似文献
8.
Briones XG Encinas MV Petri DF Pavez JE Tapia RA Yazdani-Pedram M Urzúa MD 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13524-13532
The adsorption of hydrophobically modified polyelectrolytes derived from poly(maleic anhydride-alt-styrene) (P(MA-alt-St)) containing in their side chain aryl-alkyl groups onto amino- or methyl-terminated silicon wafers was investigated. The effect of the spacer group, the chemical nature of the side chain, molecular weight of polyelectrolyte, and ionic strength of solution on the polyelectrolyte adsorbed amount was studied by null ellipsometry. The adsorbed amount of polyelectrolyte increased with increasing ionic strength, in agreement with the screening-enhanced adsorption regime, indicating that hydrophobic interactions with the surface play an important role in the adsorption process. At constant ionic strength, the adsorbed amount was slightly higher for polyelectrolytes with larger alkyl side chain and decreased with the hydrophobicity of aryl group. The adsorption behavior is discussed in terms of the side chain flexibility of the polymer. Characteristics of the adsorbed layer were studied by atomic force microscopy (AFM) and contact angle measurements. AFM images show the presence of aggregates and closed globular structure of polyelectrolyte onto the amino- or methyl-terminated surface, which agrees with a 3D and 2D growth mechanism, respectively. Fluorescence measurements showed that the aggregation of polyelectrolyte containing the hydrophobic naphthyl group occurs already in the solution. However, the aggregation of polyelectrolytes containing the phenyl group in its side chain is not observed in solution but is induced by the amino-terminated surface. This difference can be explained in terms of the higher flexibility of side chain bearing the phenyl group. The polyelectrolyte films showed a high chemical heterogeneity and moderate hydrophobicity. 相似文献
9.
M. Błachnio P. Staszczuk G. Grodzicka 《Journal of Thermal Analysis and Calorimetry》2008,94(3):641-648
Modified carbon multiwall nanotubes were prepared via the oxidation process by means of 65% nitric acid or ferric nitrate
dissolved with 65% nitric acid. Using special thermogravimetry and sorptometry methods physicochemical properties of pure
and modified nanotube surfaces were investigated. A numerical and analytical procedure for the evaluation of total heterogeneous
properties on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented.
The calculations of the fractal dimensions of carbon nanotubes using the sorptometry and thermogravimetry data is presented. 相似文献
10.
This work describes adsorption and wetting characterization of hydrophobic ordered mesoporous silicas (OMSs) with the SBA-15 motif. Three synthetic approaches to prepare hydrophobic SBA-15 silicas were explored: grafting with (1) covalently-attached monolayers (CAMs) of C(n)H(2)(n+1)Si(CH(3))(2)N(CH(3))(2), (2) self-assembled monolayers (SAMs) of C(n)H(2)(n+1)Si(OEt)(3), and (3) direct ("one-pot") co-condensation of TEOS with C(n)H(2)(n+1)Si(OEt)(3) in presence of P123 (n=1-18). The materials prepared were characterized by nitrogen adsorption, TEM, and chemical analysis. The surface properties of the materials were assessed by water contact angles (CAs) and by BET C constants. The results showed that, while loadings of the alkyl groups (%C) were comparable, the surface properties and pore ordering of the materials prepared through different methods were quite different. The best quality hydrophobic surfaces were prepared for SBA-15 grafted with CAMs of alkylsilanes. For these materials, the water CAs were above ~120°/100° (adv/rec) and BET C constants were in the range of ~15-25, indicating uniform low-energy surfaces of closely packed alkyl groups on external and internal surfaces of the pores respectively. Moreover, surfaces grafted with the long-chained (C(12)-C(18)) silanes showed super-hydrophobic behavior (CAs~150-180°) and extremely low adhesion for water. The pore uniformity of parental SBA-15 was largely preserved and the pore volume and pore diameter were consistent with the formation of a single layer of alkylsilyl groups inside the pores. Post-synthesis grafting of SBA-15 with SAMs worked not as well as CAMs: the surfaces prepared demonstrated lower water CAs and higher BET C constants, thereby indicating a small amount of accessible polar groups (Si-OH) related to packing constrains for SAMs supported on highly curved surfaces of mesopores. The co-condensation method produced substantially more disordered materials and less hydrophobic surfaces than any of the grafting methods. The surfaces of these materials showed low water CAs and high BET C constants (~100-200) thereby demonstrating a non-uniform surface coverage and presence of unmodified silica. It is concluded that CAMs chemistry is the most efficient approach in preparation of the functionalized OMS materials with uniform surfaces and pores. 相似文献
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Yu. Bolbukh V. Tertykh P. Klonos P. Pissis 《Journal of Thermal Analysis and Calorimetry》2012,108(3):1111-1119
Effects of the nature of functional groups (namely, hydroxyl, methyl, silicon hydride, amino, and vinyl) on the surface of pristine and modified silicas on polymerization of 2-hydroxyethylmethacrylate (HEMA) and on structural characteristics of the filled composites have been studied. DSC, FTIR spectroscopy and equilibrium water sorption (ESI) techniques were applied for the composites characterization. Results obtained testify that the chemical nature of the grafted groups has a strong influence on the monomer orientation in the surface layer of the filler. More uniform and cross-linked structures were detected in the composites with particularly methylated silica. Filler with chemically active silicon hydride groups promotes formation of ordered structure with rigid macromolecules. The presence of amino and vinyl groups on the silica surface results in formation of flexible polymer chains with a low cross-linking density or with a low polymerization degree, even at 2?wt% filling degree. Water uptake for composites with vinyl- and amine-containing silicas was low, indicating the close-packing of polymeric molecules in the filled polyHEMA. 相似文献
15.
Notley SM 《Journal of colloid and interface science》2012,375(1):35-40
Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI. 相似文献
16.
《Colloids and Surfaces》1988,29(4):359-371
We have developed an experimental set-up using radiolabelled proteins for the continuous measurement, as a function of time, of the excess concentration of superficial protein at a solid/liquid interface. The experimental conditions were designed in order to minimize the coupling of the interfacial interaction with bulk diffusion, and therefore to work within the limit of the interfacial interaction control. Chemical kinetics were assumed to follow a Langmuir equation. The absorption (Ka) and desorption (Kd) rate constants have been evaluated in the case of fibrinogen and albumin adsorption, onto glass beads and synthetic hydroxyapatite powder, respectively. In order to determine these parameters, a non-linear differential equation (obtained by combining the Langmuir rate equation and a mass-balance equation) was solved by the fourth-order Runge-Kutta method. The results obtained are consistent with the hypothesis of an adsorption rate controlled by the interfacial interaction. 相似文献
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18.
Lamellar crystalline silicas (crystalline silicic acids, chemical composition SiO2·xH2O; examples: H4Si14O30·xH2O, H4Si20O42·xH2O) are distinguished from the amorphous forms by their layered structure and exceptional adsorption properties. One outstanding example is the reaction with anionic surfactants. Several types of crystalline silicas (typical H4Si20O42·xH2O) can intercalate ionic pairs consisting of surfactant anion and gegen ion into the interlayer space. The saturation value of SDS adsorption is 0.475 mmol SDS/g H4Si20O42·3H2O. The acid H4Si14O30·xH2O adsorbs anionic surfactants at the external surfaces only (saturation value 0.04 mmol/g H4Si14O30·0.8 H2O). When anionic surfactants are adsorbed in the interlayer space, the layer separation increases to such an extent that the crystals disarticulate in a fan-like manner or delaminate into thinner packets of layers or smaller aggregates. Washing-out the SDS ionic pairs or drying reconstitutes the parallel layer orientation and leads to re-aggregation of the packets and fragments. 相似文献
19.
Gun'ko VM Sheeran DJ Augustine SM Blitz JP 《Journal of colloid and interface science》2002,249(1):123-133
Silica gels Davisil 633 and 643, and fumed silica Cab-O-Sil HS-5 with grafted 3-aminopropyl dimethylsilyl (APDMS), butyl dimethylsilyl (BDMS), octadecyl dimethylsilyl (ODDMS), and trimethylsilyl (TMS) groups of different concentrations were studied using the nitrogen adsorption method. Changes in the textural and energetic characteristics of modified silicas depend on features of the oxide matrices and grafted OSC. 相似文献
20.
Clark JH Macquarrie DJ Tavener SJ 《Dalton transactions (Cambridge, England : 2003)》2006,(36):4297-4309
This review focuses on recent developments in the preparation, properties and catalytic applications of chemically modified mesoporous silicas. Over the last few years, this group of materials has been the subject of intense activity in the materials community, and many applications have been found for these fascinating materials. This non-exhaustive review aims to highlight the key features of the materials, which are relevant and important to catalysis, and illustrates their utility with a series of recent examples. 相似文献